The subject matter disclosed herein generally relates to rotors for aircraft use. More specifically, the subject disclosure relates to hub configurations for tilt rotors.
Rotor blades utilized in tilt-rotor aircraft typically must be able to pitch significantly relative to a blade pitch change axis, be capable of allowing flapping motion of the rotor blades, have proper frequency placement, proper kinematic couplings, among other requirements. To meet these requirements in the past, a gimbal-style rotor hub has been utilized as shown in FIG. 7. A gimbal style hub offers the benefit of a low head moment and, consequently, less structure required to support the rotor shaft within the gearbox and less structure required to support the gearbox on the airframe. The rotor hub 100 includes a trunnion 114, a series of drive links 106, and a thrust bearing 116 arranged at an interface of the rotor hub 100 and a rotor shaft 104. The trunnion 114 is connected to the rotor shaft 104 via splines. The links 106 are connected between the trunnion 114 and to the rotor hub 100 via a number of pillow blocks 102 thereby allowing relative motion between the hub 100 and the rotor shaft 104 while transferring torque between the rotor shaft 104 and the hub 100. The trunnion 114 is located between the upper and lower thrust bearings 116. The upper and lower thrust bearings 116 are also connected to the shaft via splines and allow relative motion between the rotor hub 100 and the rotor shaft 104 while absorbing the thrust loads of the rotor. The elastomerics within the links 106 and upper and lower thrust bearings 116 are thermally limited, which limits operations of the tilt rotor and maneuverability of the aircraft in which the tilt rotor is utilized. Further, the gimbal-style hub has many parts and is of considerable weight.
Pitch change of the blades of such a rotor is typically accommodated by inboard pitch change bearing assemblies (IPCBAs) 108 and outboard pitch change bearing assemblies (OPCBAs) 110. The IPCBAs 108 are typically located in holes through the yoke 112 of the rotor hub 100, which presents structural issues for the yoke 112, as it must react IPCBA 108 shear loads. The art would well-receive a less complex, lighter weight tilt rotor hub configuration, while maintaining lower head moments than other lightweight configurations.